Combination of electrically heated transparent window and antenna



Dec. 16.. 1969 H. E. SHAW. JR 3,484,584

COMBINATION OF ELEGTRICALLY HEATED TRANSPARENT WINDOW AND ANTENNA FiledJuly- 23, 1968 3.Shee-ts-Sheet 1.

"l8 H t H a K 7 w DI F i G 2 INVENTOR HUGH ,6. SHA .41

A'ITORNEYE Dec. 16., 1969 H. E. SHAW. JR 3,434,534

COMBINATION OF ELECTRICALLY HEATED TRANSPARENT WINDOW AND ANTENNA FiledJuly 23, 1968 5 Sheets-Sheet 2 ZNVENTOR 0 F o 7 fI'UGl-f ,6. SHAWJR,

Dec. 16., 1969 H. E. SHAW. JR 3, COMBINATION OF ELECTRICALL-YTRANSPARENT WINDOW AND ANTENNA Filed July 25, 1968 s Sheets-Shem 5 l l i0 2 3 0 4 J iEg -HII 1 5 l I WI :5

a M! -O N INVENTOR AORNEYS United States Patent US. Cl. 219-522 ClaimsABSTRACT OF THE DISCLOSURE A combination antenna and heater,specifically adapted for use in an automobile. A heating circuit isconnected between a pair of bus bars disposed adjacent the oppositeedges of a heating area, such as all or part of a windshield or a rearwindow, preferably comprising an electroconductive elementinterconnecting the bus bars, is coupled to a direct current source.Means isolate the conductive element from ground, permitting theconductive element to serve also as an antenna for the automobile radio.The isolating means preferably are elements having low D.C. resistanceand high impedance at radio frequencies.

The present invention relates to a combination antenna and heater. Whilethe article described herein has particular use in an automobile window,and will be described in such an environment, it is understood that itis adaptable for use in any environment where it is desirable to have anarticle serve a dual function of heater and antenna.

It is well known to use a heating circuit in windows of automobiles oraircraft to remove fog or frost that forms on a window surface. If thewindow is laminated, the circuit comprises heating wires carried by athermoplastic interlayer. The heating wires extend between a pair of busbars that are disposed along opposite side edges of the area of thewindow to be heated. When an electric current is passed through thewires, they heat the area, thus removing any surface film of moisture orice. It is also possible to apply a transparent, electroconductive filmto one of the transparent sheets and use a current that is passedthrough the film to heat the sheet for the same purpose.

Monolithic glass or plastic transparent sheets suitable for use aswindows have been used as surfaces for supporting electroconductiveheating circuits. For example,

a pair of bus bars interconnected by either spaced heating elements,such as metallo-ceramic lines matured onto a glass surface, orelectroconductive metal oxide coatings formed by pyrolyzing a metal salton a heated glass surface have been used as heating circuits on glasssheets and vacuum evaporated metal coatings and the like have been usedon glass and transparent plastic sheets.

It has also been known to embed a wire or a series of wires or otherconductive elements in the interlayer or on the surface of one of thesheets forming a laminated windshield of an automobile or an airplaneand to connect them to a radio antenna circuit of a radio Within thevehicle to provide an antenna. However, prior to the present invention,no attempt has been made to employ the same elements that are used for aheating circuit to serve a second purpose as an antenna. The reasons forthis are obvious to any student of electricity. Radio waves which arereceived by an antenna must be effectively shielded from ground. Theheating circuit of an automobile or an aircraft utilizes the vehiclebody as a ground. Therefore, a conventional heating circuit that usesthe vehicle body as part of the circuit would ground an antenna andprevent the reception of signals to a radio circuit.

Despite the obvious difliculties of having a circuit carried by a windowserve both purposes simultaneously, the present invention has devisedmeans for isolating the high-frequency radio signals from the vehicleframe and still permit the passage of direct current from the automobilebattery supply system when desired without affecting the alternatingcurrent high-frequency signal and vice versa.

The invention will be better understood after the reader has studied adescription of certain illustrative embodiments of the present inventionwhich follows.

In the drawings which form part of the description, and wherein likereference numbers refer to like structural elements,

FIG. 1 is a schematic circuit diagram of a typical electrical circuitincorporating the gist of the present invention;

FIG. 2 is an over-all view of a monolithic glass sheet used as a curvedrear window of an automobile, wherein the electroconductive circuit issupported directly on a glass surface of said rear window;

FIG. 3 is a sectional view taken along the lines IIIIII of FIG. 2;

FIG. 4 is an over-all view of an alternate embodiment of the presentinvention wherein the electroconductive circuit is carried by theinterlayer of a laminated glassplastic assembly typical of an automobilewindshield;

FIG. 5 is an enlarged fragmentary sectional view of a portion of thelaminated windshield of FIG. 4, showing how heating wires forming partof the electroconductive circuit are embedded in the interlayer of thelaminated windshield;

FIG. 6 is an enlarged view taken along the lines VIVI of FIG. 4;

FIG. 7 is an enlarged view taken along the lines VIIV1I of FIG. 4, and

FIG. 8 is a schematic circuit diagram showing use of the heater-antennacombination in a vehicle provided with an AMFM radio.

Referring to the drawings, an electroconductive circuit 11 is shown inFIG. 1. The circuit comprises a battery 12, a switch 13, a pair oflow-DC resistance coils 14 and 15 interconnected to one another throughan electroconductive element 16 comprising lines of electroconductivematerial.

A pair of bus bars 18 and 19, extending across the opposite margins ofthe heating area, are in electrical contact with the opposite ends ofthe lines of electroconductive material 16. In addition, a lead line 17forms a branch from bus bar 18 to a radio receiver 20.

A lead wire 24 connects bus bar 18 to a coupling 25. An additional leadwire 26 connects bus bar 19 to an additional coupling 27. Coupling 25connects the lead wire 24 to two wires, one of which is the antenna leadwire 17 and the other of which is connected to the coil 14 and via thebattery switch 13 to the hot terminal of the battery 12. The latter isgrounded at its negative terminal. It is also acceptable to reverse thepolarity of the battery 12 so that battery switch 13 is connected to thenegative terminal of the battery and its positive terminal is grounded.

In order to isolate the radio antenna from the ground (depicted as aterminal 29), the coils 14 and 15 are interposed between both ends ofthe antenna heating circuit 11 and the ground. To accomplish this end,coil 14 is coupled to ground at its end remote from the end coupled tobus bar 18, and coil 15 is grounded at its end remote from the endcoupled to bus bar 19.

While coils 14 and 15 have very small resistance to direct current, theyhave a large impedance to alternating current, particularly at radiofrequencies. It will thus be seen that the coils 14 and 15 act as highimpedances to isolate the radio antenna circuit from the ground forsignals of radio frequency. However, when the battery switch 13 isclosed, coils 14 and 15 present a very low resistance to the DC powerfeeding current into the heating wires 16 through the bus bars 18 and19. This permits the circuit 11 to serve as both a radio antenna and aheating circuit to remove moisture, such as fog or ice, from the surfaceof a window on which it has deposited.

Since the electromotive lines 16 and the bus bars 18 and 19 arepreferably composed of a ceramic silver material, and the lead-in wires24 and 26 are composed of a copper braid having a much highercoefficient of thermal expansion than the ceramic silver, it has beenfound most beneficial to spot solder the copper lead-in wires 24 and 26at spaced intervals 28 along the length of the bus bars, leaving thecopper wires sufficiently loose between the spaced solder points toenable the copper and the ceramic silver to change their dimensions atdifferent rates in response to the changes of temperature that resultfrom actuating or deactivating the heating circuit without inducingstress that weakens the bonds between the lead-in wires and the busbars.

In commercial embodiments of the invention such as automobile rearwindows or backlights, the resistance heating elements 16 and the busbars 18 and 19 are formed of a typical ceramic conductive coatingmaterial comprising a highly conductive metal powder, such as silver,and a vitrifying binder. Typical ceramic conductive coating compositionswhich may be used may have the following compositions:

COMPOSITION I COMPOSITION III A typical commercial composition is amixture containing 90 percent by weight of a ceramic silver compositionsold under the trade name AB Silver by the OHommell Company of Carnegie,Pennsylvania, and percent of a nonconducting mixture of metallic oxidessold under the trade name K 736 Black by the Ferro Corporation ofCleveland, Ohio.

The electroconductive stripes 16 form narrow lines approximately inchwide and the bus bars 18 and 19 form transversely extending rowsinterconnecting the ends of the stripes 16 in widths of A inch. Thesilver ceramic mixture is preferably applied through a stencil to formthe stripes 16 and the bus bars 18 and 19 by a process known as silkscreening to form a pattern .0005 inches thick on a surface of anautomobile rear window or backlight.

The particular material described has an electrical resistance of 0.35ohms per linear inch along the electroconductive stripes 16 whereas thebus bars 1 8- and 19 so deposited have an electrical resistance of 0.04ohms per linear inch along their length. When the backlight to be coatedwith such a design is rectangular or a quadrilateral havingsubstantially straight and parallel upper and lower .4 longitudinaledges, the elongated electroconductive heated stripes 16 are spacedabout one inch apart and are parallel to one another and straight. Whenthe upper and lower edges of the backlight are bowed or are of differentconfigurations from one another, automotive stylists prefer theelongated electroresistant heating stripes 16 to extend between theopposed bus bars 18 and 19 in slightly changing paths, the uppermoststripe conforming in curvature substantially to the curvature of theupper longitudinal edge of the backlight and the lowest elongatedelectroconductive heated stripe conforming to the shape of its loweredge.

The ends of adjacent stripes 16 at their points of contact with the busbars are spaced approximately one inch from the adjacent stripeconnected to the same bus bar and the configuration of the intermediatestripes is graduated from stripe to stripe to provide a gradual changefrom the configuration of the uppermost stripe to that of the loweststripe. The heating pattern resulting from subjecting the opposite busbars 18 and 19 to a potential difference of 12 volts results in asubstantially uniform heating pattern of about 25 to 30 watts per squarefoot throughout the entire extent of the vision area of the backlight.

To protect the heating element and bus bars from excessive exposure toatmospheric conditions, the stripes 16 and bus bars 18 and 19 are allapplied to the inner surface of the backlight when installed. Under suchcircumstances, no protective coating has been found necessary.

The stripes 16 and the bus bars 18 and 19 are applied simultaneouslythrough the silk screening technique described previously. The coatedglass sheet is then mounted on a bending mold having an outline shapingrail of concave elevation conforming in elevation and outline but ofslightly smaller area than the glass sheet after bendmg.

The glass laden mold is introduced into a furnace where the glass isheated to a temperature sufficient to sag the glass sheet intoconformity to the mold shaping surface. During this heating, the finelydivided metal ceramic frit fuses onto the glass surface which facesupward and which becomes curved concavely during the bending operation.When the glass bending is completed, the glass sheet is removed from thehot atmosphere and chilled as rapidly as possible to produce a temperedglass sheet. Since the stripes 16 and the bus bars 18 and 19 have fusedonto the upper, concave glass surface during the heating operation, theyremain in the exact configuration in which they were applied to the coldglass through the stencil in the silk screening process when the glassis chilled.

Preferably, each lead-in wire is a flat copper braid of suflicientcurrent carrying capacity, such as the equivalent of No. 14 solid copperwire, to minimize any loss of power in the bus bars which result inheated bus bars rather than the heat being dissipated throughout theextent of the stripes 16. The free ends of the lead-in wires 24 and 26are loosely laid over the attached ceramic silver bus bar 18 or 19 andattached to its adjacent bus bar by spaced solder connections 28,preferably at about 2 inch intervals. For example, a flat tin copperbraid sold as Preparation No. 1231, equivalent to N0. 14 AWG, made bythe Alpha Wire Corporation of Elizabeth, N.I., is soldered to theceramic silver bus bars 18 and 19 using a tin-lead-silver soldercontaining 70 percent by weight of lead, 27 percent of tin and 3 percentof silver, sold by the Belmont Smelting and Refining Company ofBrooklyn, N.Y. as No. 5701 solder. A suitable flux for the solder issold under the trade name Nokorode solder paste made by the M. W. DuntonCompany of Providence, RI.

The multiple attachments of the lead-in wires to each of the bus barsreduces the length of the current path through any part of the bus barto a reasonable distance which does not cause undue loss of electricalenergy to heat the bus bars. The looseness of the attachment of thelead-in wires to the bus bars permits the lead-in wires to extendloosely between the spaced connections 28. At the same time, only theportions of lead-in wires 24 and 26 that are not disposed over the busbars 18 and 19 are covered with insulation 30. This increases the areaof contact between the lead-in wires 24 and 26 and the bus bars 18 and19 to reduce the heat loss in the bus bars even further, thus enablingthe heating elements 16 to provide as large a proportion of the totalresistance of the heating circuit as possible.

As stated previously, the use of the high impedance, low-resistancecoils 14 and 15 in the circuit as depicted in FIG. 1 isolates the radioantenna circuit from ground at radio frequencies. Thus, whenever theradio receiver is operated, the coils 14 and 15 isolate the radioantenna circuit from ground and permits the circuit 11 comprising busbars 18 and 19 and the electroconductive elements 16 to serve as a radioantenna by its connection to the radio antenna circuit 20 through theantenna wire 17, regardless of Whether the circuit 11 is connected tothe battery 12 by closing the battery switch 13.

The embodiment depicted in FIGS. 4 to 7 shows a laminated windshield 30comprising a first glass sheet 32, a second glass sheet 33 and athermoplastic interlayer 34 of a material such as plasticized polyvinylbutyral bonded between the glass sheets. Electroconductive wires 35 of amaterial such as nichrome or tungsten or the like are embedded on thesurface of the plastic interlayer 34 and extend between a pair ofelectrodes or bus bars 36 and 37 extending adjacent the oppositeelongated side edges of the area of the interlayer 34 to be heated.

The glass sheets 32 and 33 and the interlayer 34 have matched curvaturesand substantially identical outlines except for a notched portion 38along each longitudinally extending side margin of the glass sheet 33.The notched portion has a laterally dimension sufficient to enable it toextend laterally inward of the inner boundary of the bus bar 36 or 37.

Wires 35 have a small diameter, .0002 inch to .002 inch being preferred.They are arranged in parallel, substantially equidistant, arrangement,about 8 to 12 to the inch, and extend from bus bar 36 to bus bar 37. Thebus bars are preferably thin strips of conductive metal, such as copper,superimposed over the opposite ends of the wires 35. The copper stripsare about inch wide and about .005 inch thick and extend with theirouter sides about A inch inside the windshield margin.

An angle member 41 of moisture-impervious material, such as a thin bentsheet of aluminum, encloses the notched portion 38 to form a chamberthat is filled with a resin 42, as will be described later. Member 41comprises a solid wall 44 parallel to a major surface of the laminatedwindshield 30 and an apertured, slotted wall 46 disposed at an angle tothe solid wall 44 to engage the edge surfaces of glass sheets 32 and 33.A layer of pressure sensitive adhesive 48 is located on the innersurfaces of the walls 44 and 46. The angle member 41 is slightly longerthan the notched portion 38, with solid wall 44 slightly higher than thewidth of the notched portion and apertured slotted wall 46 having awidth substantially equal to the thickness of the laminated windshield30. v

Bus bars 36 and 37 are adhered by pressure and an adhesive comprising athin film of polyvinyl butyral dissolved in chloroform along the lengthadjacent the opposite sides of the interlayer including the portion ofthe interlayer that faces the notched portions 38. Each bus bar 36 or 37has a width slightly less than that of the notched portion so that itsouter edge is recessed within the outer edge surface of the portion ofthe glass sheet 32 that faces the notched portion 38 adjacent thereto.

A lead-in wire 39 similar to lead-in wire 24 is soldered to bus bar 36within the notched portion 38 along the upper edge of the windshield 30,while a lead-in wire 40 similar to leadin wire 26 is soldered to the busbar 37 within the notched portion 38 along the lower longi- 6 tudinaledge of the windshield 30. The lead-in wires 39 and 40 are encased withinsulation except for their free inner ends. The uninsulated free endsare soldered to the bus bars 36 and 37, respectively. Theelectroconductive wires 35 have their ends in electrical contact withthe bus bars 36 and 37. Therefore, the bus bars 36 and 37 serve as meansto connect the lead-in wires 39 and 40 to the antenna or heating wires35.

The chamber, defined by the notched portion 38, is filled with a filler42 of moisture-resistant, electrically insulating material. This may bea preformed member of an insulation material such as a fiber glassreinforced resin coated with a pressure sensitive adhesive, for example.However, such a preformed member must conform exactly in shape to thatof the notched portion 38 containing the lead-in wire to bus barconnection. The technique to be described immediately below has beenfound to be most suitable for insulating the exposed wires and theirconnecting means from electrical contact with the metal frame during atest simulating mass production.

With particular emphasis on FIGS. 6 and 7, the apertured slotted wall 46is provided with a centrally disposed slot 54 of just sufiicient widthto provide clearance to enable the angle member 41 to fit over thelead-in wire 39 or 40 when the angle member is applied against thecentral portion of one of the edges of the windshield to encompass thenotched-out portion 38 of the notched glass sheet. In addition,apertures 56 and 58 are provided in the apertured slotted wall 46. Oneof the apertures is used for injection molding a rapidly setting resinof electrical insulation material, while the other aperture and the slot54 permit air to escape from the chamber when the resin is injected.

The article described above is made in the following manner. A pair ofglass sheets 32 and 33 are mounted in superimposed relation with asuitable parting material disposed between the sheets. Sheet 33 havingthe notchedout portions 38 is disposed below sheet 32. The two glasssheets are usually made of plate glass or float glass of commercialsoda-lime-silica composition. The two sheets are superimposed in themanner recited in bending relation to a glass bending mold having anupward facing outline shaping surface of concave contour in elevation.The glass laden mold is exposed to sufficient heat to cause the glasssheets to conform to the upward facing shaping surface of the bendingmold.

After the sheets have bent to the desired curvature and cooled accordingto a controlled pattern of cooling, they are removed from the bendingmold and are assembled to form a sandwich with a sheet of plasticizedpolyvinyl butyral having the antenna wires embedded therein with excesswire extending from the plastic. The wires are embedded in the plasticsheet 16 by a battery of hot needles. A typical technique for sewing athin wire into a sheet of insulating material, such as the plasticinterlayer sheet 34, is shown in US. Patent No. 2,813,960 to Egle andBethge. While the wires 35 are shown as extending in straight lines,they may be sewn in sinuous configuration to reduce any diffractionpatterns if desired.

After the glass-plastic sandwich has been assembled with the bent glasssheets on opposite sides of the wirecontaining plastic interlayer, theassembly is subjected to a commercial laminating operation. A suitableoperation is described and claimed in US. Patent No. 2,948,645 toLaurence A. Keim, assigned to PPG Industries, Inc. This laminatingmethod comprises first enclosing the periphery and margin only of theassembly within a flexible, channel-shaped member made of afluidimpervious material to form a conduit adjacent the periphery of theinterfaces between the interlayer and the bent glass sheets, evacuatingair from the conduit to remove air from between the interlayer and theglass sheets, continuing the evacuation while heating the enclosedassembly in a furnace at a temperature between about 150 degreesFahrenheit and 350 degrees Fahrenheit with the furnace at substantiallyatmospheric pressure, removing the channel-shaped member when themarginal portion is bonded, and subjecting the assembly to a finallamination at a pressure of between about 100 and 250 pounds per squareinch at a temperature between about 190 and 325 degrees Fahrenheit untilthe entire area of the assembly is clear.

After the assembly is laminated, it is cleaned with particular carebeing taken to remove oil from the notched portion of the assembly incase the final larninating step is performed in an oil autoclave. Anyexcess plastic is trimmed and the plastic edge sealed more intimately tothe glass surfaces by edge rolling. US. Patent No. 2,999,779 to John W.Morris shows a typical edge rolling process and apparatus. Then, thelead-in wire 39 or 40 is carefully soldered to the exposed surface ofbus bar 37.

The angle member 41 is then adhered by the pressure sensitive adhesive48 to abut against the windshield 11 and completely cover the notchedportion 38. In doing so, the slot 54 slides around the lead-in wire 39or 40 to form the chamber defined by the notched portion 38. Suitableadhesives include plasticized polyvinyl butyral, and any of thefollowing commercially available materials sold under the followingtrade names by the following corporations: Poly EM sold by Gulf OilCorporation of Pittsburgh, Pennsylvania; Eastman 910 sold by EastmanKodak Corporation of Rochester, N.Y.; and Tackmaster 1477 sold by PPGIndustries, Inc. of Pittsburgh, Pa.

The angle member 41 is preferably formed of any material that ismoisture impervious. Thin aluminum sheeting has been found to be quitesuitable. For a typical notched portion 2 inches long and about 0.4 inchwide, a partially tempered, flat aluminum sheet 3 /2 inches long andinch wide is perforated to form the apertures 56 and 58 and the slot 54and then bent along an axis extending lengthwise of the sheet to form aslotted, apertured wall 46 having a width of A inch and a solid wall 44having a width of /2 inch. Other suitable materials are lead foil tape,copper sheeting, and the like.

After the windshield has passed an optical inspection and the anglemember 41 has been secured to the windshield 30 to convert the notchedportion 38 into an enclosed chamber, the windshield is oriented withholes 56 and 58 of the angle member 41 facing upward and the filler 42of electrical insulator material is injection molded through one of theapertures 56 or 58 of the angle member 41. A rapidly curing,water-resistant reisn is used, such as polysulfide resin called Thiokolsold by the Thiokol Chemical Corporation, Bristol, Pa., or a roomtemperature vulcanizable silicone, such as 615 RTV silicone supplied 'byGeneral Electrical Company, Schenectady, N.Y., or Scotchcast 225electrical resin sold by Minnesota Mining and Manufacturing Company, St.Paul, Minn. Any filler material having the ability to set within 24hours is termed a rapid setting material for the purposes of filling thechamber with insulation.

When excess resin flows out through the other aperture 58 and thecentrally disposed slot 54, the chamber enclosed by the walls 44 and 46of the angle member 41 is completely filled with resin 42. Any excessresin that is inserted in a chamber oriented with its apertures facingupward forms small mushroom-shaped domes that mechanically lock theangle member in place. The resin provides sufficient insulation toinsulate the free uninsulated end of the insulated lead-in wire 39 or 40as well as the connecting means comprising the bus bar and the heatingwires from any electric connection with the metal of the automobile bodyin which the windshield is to be installed.

A second injection molding operation is preferably conducted to till theopposite notched portion after soldering the other lead-in wire 40 or 39to bus bar 36 or 37, respectively and after the laminated Windshieldshave been mounted on a shipping pallet for shipping with the Windshieldsoriented so that the opposite notched portion 38 to be filled with resinfaces upward. The materials suitable for the filler have a short potlife on the order of a few hours, subject to variation depending on thechoice and quantity of accelerator used as explained in the literatureof the suppliers of these materials. After 24 hours, these materials aresufficiently set so that the windshields can be transported withoutdanger of the system losing its moisture-resistant characteristics. Itis necessary that the racks be stored for sufficient time for the resinto set before the Windshields in the pallet are installed. To be on thesafe side, each rack containing a number of Windshields is permitted tostand overnight after the injection molding operations take place toensure that the resin is set before the rack of Windshields is shipped.

In a typical circuit for an AM and/ or FM radio conforming to thepresent invention using a 12 volt system for an automobile and a heatingarea about 24 inches by 48 inches, wherein the bus bar to bus barresistance is about 0.8 ohms, coils 14 and 15 are radio frequency chokescomposed of air wound coils of insulated varnished coated number 15copper wire wound in 2 layers having about 150 turns along a length ofab ut 6 inches.

In automobiles provided with FM radios only, it has been found that theheating circuits 11 behave as antennas for the FM radios even in theabsence of the coils 14 and 15. The wiring in the system can providesufiicient inductance to isolate the FM radio antenna circuit fromground sufliciently to receive signals from FM stations.

Since many automobiles are provided with AM-FM radios, in order toprovide a complete disclosure, FIG. 8 shows an alternative embodiment ofa circuit that incorporates a combination heater and antenna for AM-FMradios for automobiles. According to the present invention, FIG. 8represents an electrical circuit that isolates the radio antenna circuitfrom the ground while allowing the antenna to serve as a heater whensubjected to direct current, as in the first embodiment, andincorporates means to switch wave bands.

The heating and antenna circuit 11 of FIG. 8 comprises elongatedelectroconductive elements 16 connected in parallel between bus bars 18and 19 as in FIG. 1'. The antenna lead wire 17 connects the elements 16to an AM- FM radio antenna circuit 120 through the bus bar 18 and isisolated from ground by a slightly different arrangement than thatdepicted in FIG. 1.

The grounded battery 12 has its positive terminal coupled through anAM-FM switching circuit 61 to bus bar 18, which also is connected to theantenna lead wire 17, while the grounded terminal of battery 12 iscoupled to bus bar 19 through another AM-FM switching circuit 62 and thegrounded connections to the body of the automobile.

Switching circuit 61 comprises a tuner T3 permanently tuned broadly tothe middle of the AM band in one parallel branch 64 and another tuner T4permanently tuned broadly to the middle of the FM band in another paralel branch 66. Switching circuit 62 comprises a tuner T1 permanentlytuned broadly to the middle of the AM band 111 one parallel branch 67and another tuner T2 tuned broadly to the middle of the FM band inanother parallel branch 68.

Each of the tuners T1 through T4 comprises an inductance and acapacitance of selected size for the tuning desired arranged inparallel. For example, tuners T1 and T3 for AM tuning tuned for 1000kilocycles per second may comprise a capacitor of 51 micromicrofarads ofcapacitance in parallel with a coil having 500 microhenries ofinductance while the FM tuner circuits T2 and T-4 tuned for megacyclesper second may comprise a capacitor of 12.7 micromicrofarads capacity inparallel with a coil having an inductance of 0.2 microhenries or mayconsist of a wire having the requisite inductance at the desiredfrequency.

Switch SW-l has a contact 77 for connecting tuner circuit T-1 in branch67 to bus bar 19 and a contact 78 to connect tuner circuit T2 in branch68 to bus bar 19. Switch SW-Z has a contact 74 for connecting tunercircuit T-3 in branch 64 to bus bar 18 and another contact 76 to connecttuner circuit T-4 in branch 66 to bus bar 18. The two switches SW-l andSW-2 are mechanically coupled to simultaneously connect both of the AMtuning circuits T-1 and T-3 to bus bars 19 and 18, respectively, throughcontacts 77 and 74, respectively, in one position when the radio 120 istuned to an AM wavelength. When the switches SW-l and SW-2 are switchedto contacts 78 and 76, respectively, the FM tuning circuits T-Z and T-4in branches 68 and 66, respectively, replace the AM tuning circuits T-1and T3 in the circuits that connect to the bus :bars. The tuning circuitarrangement thus isolates from ground the radio antenna circuitregardless of whether the radio 120 is tuned to the AM or FM broadcastband.

In this embodiment, each pair of tuning circuits, either the onecomprising AM tuning circuits T-1 and T-3 or the one comprising FMtuning circuits T-Z and T-4, serve the same function as the coils 14 andin the FIG. 1 embodiment. Switching the switches SW-1 and SW-Z in unisonenables the radio to receive signals in either the AM broadcast band orthe FM broadcast band through the electroconductive circuit 11 which iseffectively isolated from the ground.

While the tuner circuits of the FIG. 8 embodiments have been describedas having fixed tuning, it would be a simple matter to make use ofadjustable inductances and/or adjustable capacitors capable of tuning tothe exact frequency to which the radio is tuned. Under suchcircumstances, the radio listener adjusts the tuning circuits T-1 andT-3 or T2 and T-4 in unison to obtain maximum impedance which results inmaximum strength of signal received. More specifically, branches 67 and64 may contain adjustable tuning devices T-1 and T-3 suitable for the AMband, while branches 68 and 66 contain adjustable tuning devices T-Z andT-4 suitable for the FM band. This adjustable tuning enables the antennato receive a strong signal for the radio receiver at any frequency inits respective wave band as long as the tuning devices are properlytuned and the switching devices SW-1 and SW-Z are suitably switched tothe proper band (AM or FM) desired.

In most locations, coils 14 and 15 are suitable for AM reception withoutany adjustment. The FIG. 8 embodiment is usually sufiicient to obtain asignal that is equivalent to that received by a typical pole antenna inits retracted position. The FIG. 8 embodiment, when properly tuned usingadjustable reactances and/or capitances in the respective tuningcircuits, develops a signal equivalent to that obtained by partiallyextending the pole-type antenna presently used.

While the devices described above disclose the use of a pair of fixedimpedance chokes, tuned chokes and tuned circuits for isolating theradio antenna circuit from the source of potential for the heatercircuit, it is understood that other systems are also possible to enablean electroconductive element to serve as both an antenna at radiofrequencies and an electroresistant heating element of a direct currentcircuit. For example, the 12 volt battery operated system may begrounded by a separate bus bar that is insulated from the metal vehiclebody which serves as a ground for the antenna or if the automobile bodyis a non-conductor electrically, such as one made of fiber glass, a wireradio antenna ground may be insulated electrically from a separate Wireground for the batteryoperated direct current system.

The form of the invention shown and described in this disclosurerepresents certain preferred illustrative embodments thereof. It isunderstood that various changes may be made, such as using a glass sheetsurface rather than the interlayer to support the electroconductiveelements in a laminated glass unit or orienting the electroconductiveelements in any orientation desired regardless of the monolithic orlaminated nature of the window, for example, without departing from thespirit of the invention as defined and claimed in the subject matterwhich follows.

What is claimed is:

1. In combination, a transparent window having an area to be heated, anelectroconductive circuit comprising a pair of spaced bus bars extendingadjacent a spaced pair of opposite side edges of said area, and anelectroconductive element interconnecting said bus bars, a leadin wireconnected to each of said bus bars, and electrical isolating meanshaving high impedance to alternating current at radio frequencies andsmall resistance to direct current coupled to each of said lead-inwires, said combination serving as a combination antenna and windowheater when one of said electrical isolating means is grounded and theother of said electrical isolating means is coupled to a DC. source, anda radio antenna circuit is electrically connected in parallel to acircuit comprising said electroconductive circuit and said groundedisolating means.

2. The combination as in claim 1, wherein said electroconductive elementinterconnecting said bus bars comprises a series of substantiallyparallel lines of electroconductive material.

3. The combination as in claim 1, wherein said bus bars and said linesof electroconductive material are attached to a surface of said window.

4. The combination as in claim 3, wherein said window is composed of amonolithic glass sheet.

5'. The combination as in claim 2, wherein said window comprises a pairof glass sheets laminated to opposite sides of a transparent,thermoplastic interlayer and said lines of electroconductive materialare supported by said interlayer.

6. The combination as in claim 2, wherein said bus bars extend indirections transverse to the length of said area along the oppositelongitudinal edges of the area and said lines of electroconductivematerial extend substantially lengthwise of said area.

7. The combination as in claim 2, wherein said bus bars extendsubstantially lengthwise of said area along the opposite lateral edgesof the area and said lines of electroconductive material extendtransversely of said area.

8. The combination as in claim 1, further including means to adjust saidhigh impedance means in response to the wave length at which said radiois tuned.

9. The combination as in claim 1, each of said isolating means includingparallel branches tuned to the AM and FM frequency band, respectively,and means for simultaneously switching from one of said parallelbranches to the other of said parallel branches of each of saidisolating means so that one branch of each of said isolating means issimultaneously tuned to the same frequency band as a correspondingbranch of the other of said isolating means.

10. In combination, a transparent window having an area to be heated, anelectroconductive circuit comprising an electroconductive element facingsaid area, and a source of potential of sufficient magnitude to defogsaid area when connected to said electroconductive circuit, a pair ofelectrical isolating means comprising an isolating means connected toeach side of said electroconductive element, electrically conductivemeans to connect said electroconductive element in series to said sourcethrough said pair of electrical isolating means to form a heatingcircuit, electrically conductive means to connect said electroconductiveelement to a radio antenna circuit in such a manner that said radioantenna circuit is in parallel to said electroconductive element and oneof said electrical isolating means, said electrical isolating 11 meanselectrically isolating said radio antenna circuit from said source ofpotential to enable said electroconductive element to servesimultaneously as a heater and as an antenna.

References Cited UNITED STATES PATENTS 2,787,696 4/1957 Karp et al219-203 2,806,118 9/1957 Peterson 219-203 2,947,841 8/1960 Pickles et al343-704 X 1 2 2,992,313 7/1961 Taylor 343-704 X 3,409,759 11/ 1968Boicey et a1. 219-522 FOREIGN PATENTS 730,131 1/ 1943 Germany.

VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R.

